fix(discord): propagate role_authorized flag so DISCORD_ALLOWED_ROLES works end-to-end

DISCORD_ALLOWED_ROLES was checked by the Discord adapter (_is_allowed_user)
but gateway._is_user_authorized only read DISCORD_ALLOWED_USERS, so
role-authorized users were rejected with "Unauthorized user" at the
gateway layer despite passing the adapter gate.

- Add role_authorized: bool = False to SessionSource
- Add role_authorized param to build_source (base.py)
- Compute _role_authorized in on_message when user passes via role not user ID
- Thread _role_authorized through _handle_message -> build_source
- Check source.role_authorized early in _is_user_authorized (run.py)

Fixes #33952

gateway/platforms/base.py

@@ -4651,6 +4651,7 @@ class BasePlatformAdapter(ABC):
         guild_id: Optional[str] = None,
         parent_chat_id: Optional[str] = None,
         message_id: Optional[str] = None,
+        role_authorized: bool = False,
     ) -> SessionSource:
         """Helper to build a SessionSource for this platform."""
         # Normalize empty topic to None
@@ -4671,6 +4672,7 @@ class BasePlatformAdapter(ABC):
             guild_id=str(guild_id) if guild_id else None,
             parent_chat_id=str(parent_chat_id) if parent_chat_id else None,
             message_id=str(message_id) if message_id else None,
+            role_authorized=role_authorized,
         )
     
     @abstractmethod